In recent years, for flat panel display devices such as liquid crystal display devices and organic electroluminescent (EL) display devices, thermo compression bonding performed using anisotropic conductive films (ACFs) has been employed to connect a display panel substrate and a chip on film (COF) substrate on which a driver integrated circuit (IC) is mounted and to connect the COF substrate and a printed circuit board. Here, an ACF is a material which is a mixture of conductive particles and an adhesive formed into tape shape. By ACF boding, an ACF is placed between terminal portions of different substrates, and thereafter subjected to thermo compression. Consequently, terminals of the substrates in the vertical direction are electrically connected via conductive particles, and simultaneously terminals of the respective substrates are insulated from one another, and then the substrates are bonded by the adhesive being cured. Such ACF bonding can be used as a substitute for connector connection, and achieves connection with a greater number of pins, with a lower height, and at a finer pitch than connector connection.
If thermo compression bonding is applied to edge portions of a COF substrate so as to connect a printed circuit board and the COF substrate by ACF bonding and to connect the COF substrate and a display panel substrate by ACF bonding, it is difficult to obtain great strength of connection. In addition, the COF substrate is flexible, but nevertheless the COF substrate has rigidity to a certain extent. Accordingly, if, for example, the COF substrate is repeatedly deformed by heat expansion/contraction of the connected substrates and other causes, the deformation stress may cause detachment of an edge portion of the COF substrate to which thermo compression boding has been applied.
In view of this, Patent Literature (PTL) 1 discloses a technique of preventing detachment of an edge portion of a film of a COF substrate from a printed circuit board or from a liquid crystal display panel. Specifically, providing an opening in the COF substrate decreases the rigidity of the film of the COF substrate and increases flexibility of the film so that the film receives less deformation stress, thus preventing the film from becoming detached.